Help fixing Orion HCCA 225 Digital Reference

[Chopperbuilder]

I have an old Orion HCCA 225 I bought new back in the 90's. The amp stopped working about two years after I bought it. Been sitting in my basement ever since. Decided to try to fix it recently. Hooked it up and it powers up but barely put any sound out. It then burned up one of the resistors. Replaced the resistor but it burns up the new resistor. At that point I replaced all the transistors on that circuit but it still burns up the resistor. Looking for ideas of what might be causing the problem. Greatly appropriate any help!


I attached some pics of it showing the resistor.

 

[Perry Babin]

Is that resistor part of the protection circuit? If so, check the TO-92 case transistors in that area. Are all of the emitter resistors in that area within tolerance?

 

[Chopperbuilder]

I'm not sure if it is part of the protection circuit or not. I attached some more pics to show more of the circuitry that it powers.

 

[tsmith1315]

With that hot spot on the bottom of the board, I'd be highly suspicious of those electrolytics.

 

[Chopperbuilder]

The thing that puzzles me about that hot spot is there is nothing on the other side of the board directly above it.The electrolytics are close but not directly above it. If you look at that pic the you can see where the electrolytics sit slightly more towards the top of the pic..Do you think they still could have caused it?

 

[tsmith1315]

I didn't look close enough. That spot is in between the caps and that last emitter resistor for the right channel.

Take Perry's advice, he's golden.

BTW- personally, I wouldn't power that amp up without having those transistors pressed very firmly against the heatsink, all screws in place.

 

[Perry Babin]

Pull and check the transistor with the yellow arrow.

If you scrape the burned spot, how deeply is it burned?

 

[Chopperbuilder]

I was able to rub a lot of it off with a rag and a little alcohol. Scratched into it a little too. As I was saying, I'm questioning if it is a burn mark. Looks to me like ink that had gotten smudged... possibly a number...???

 

[Chopperbuilder]

Thanks Perry. I'll pull and check that transistor tomorrow.

 

[Chopperbuilder]

I got to looking at the CAP's this morning and realized they where bulging some. I replaced all of them. While I was at it, I also replaced the transistor and it's mate that Perry suggested checking. There is now once again life in the old dog!!! It's working great! Thank you Perry and Tim for your help.